The proposed experiments in Project 0002 will assess the impact of challenges to DA systems on the natural decline of these systems that accompany the aging process. Reductions in glial cell derived neurotrophic factor (GDNF+/-) or brain-derived neurotrophic factor (BDNF+/-) via gene deletion and methamphetamine (METH) exposure all produce long-term alterations in DA neural system structure and/or function. The general working hypothesis for the proposed experiments is that the interaction of repeated METH with either GDNF or BDNF reduction will exacerbate the structural and functional changes of DA systems that accompany the aging process. To test this hypothesis, male and female GDNF+/- or BDNF+/- mice exposed to METH as young adults will be examined at 3, 12, 18, and 24 months of age. Effects of these treatment combinations on DA systems will be examined using two strategies: (1) Immunocytochemical staining procedures will be used to assess the integrity of DA and medium spiny striatal neurons and whether the anti-inflammatory drug, minocycline, will block METH toxicity, (2) gene expression experiments (Affymetrix GeneChips and in situ hybridization) followed by the assessment of relevant proteins by immunoblotting will be used to identify changes in the functional properties of the DA neurons. The results of these experiments will integrate with the microglia experiments described in Project 0003 and the DAT and VMAT2 evaluations of Project 0004 to provide information about how some likely genetic and environmental factors might contribute to the different rates of declining DA function noted in the aging population. The significance of these studies is that they will determine whether a mutation in a genetic susceptibility factor (either GDNF or BDNF) combined with a commonly encountered environmental insult (METH) exacerbates the age-related decline of the dopamine systems. This investigation has the potential to identify associated genes and proteins that can be manipulated and re-introduced into the model in the future in order to attenuate the impact of multiple insults on the decline of dopamine neuronal function during aging.